Device to Device (D2D) communication and Vehicle to X (V2X) Internet of vehicles communication have become hotspot fields for development of wireless communication technologies, where V2X includes Vehicle to Vehicle (V2V) communication, Vehicle to Infrastructure (V2I) communication, Vehicle to Pedestrian (V2P) communication and the like.
D2D communication may be applied to novel services such as a social network, shopping entertainment, rescue and relief and the like. In V2V communication, through wireless communication between multiple On Board Units (OBUs), sensing information of a vehicle-borne radar, a camera and the like (i.e., sensor sharing) may be shared between vehicles and thus sensing ranges of the vehicles are extended from a line-of-sight range of dozens of meters to a non-line-of-sight range of hundreds of meters, thereby greatly improving driving safety of the vehicles and effectively implementing aided driving and automatic driving. V2I communication is another communication mode of the V2X system, and is used for communication between an OBU and a Road Side Unit (RSU); the RSU is a device with a function of a V2X terminal, for example, an intelligent traffic light and a traffic billboard, and may provide intelligent traffic information for the OBU to improve traffic efficiency of a vehicle mounted with the OBU. In an existing V2X system, V2V and V2I adopt the same design in terms of wireless communication but transmit different services, and the two modes work autonomously.
A main technical challenge, with which D2D and V2V communication is confronted, is a problem about interference suppression and congestion control between multiple terminals. Particularly, a V2V system is required to support hundreds of vehicles to simultaneously transmit sensor sharing information within a range of hundreds of meters while keeping a very low delay and very high data transmission reliability, so that a V2V resource scheduling technology capable of effectively suppressing interference between the terminals is needed. An original Institute of Electrical and Electronics Engineers (IEEE) 802.11p V2V technology may only use a pure Ad Hoc networking and scheduling scheme, namely using a self-organization mechanism such as Listen-Before-Talk (LBT) for resource scheduling on the basis of distributed cooperation between D2D or OBU terminals, to avoid resource conflict. However, such a completely centerless scheduling scheme is lower in efficiency, and along with increase of the number of terminals, the communication delay may be gradually increased and the transmission success rate may also be gradually reduced.
The Long Term Evolution (LTE) V2X technology under research and standardization of the 3rd Generation Partnership Project (3GPP) may perform centralized scheduling on V2V terminals with a base station of an LTE cellular network to greatly improve V2V transmission efficiency, reduce the V2V transmission delay and increase the transmission success rate.
Such a scheduling technology combining centralized scheduling of the base station and self-organized scheduling of Ad Hoc has been adopted in a 3GPP Release 12 (R12) LTE D2D (based on communication between LTE terminals) standard, and thus a concept of sidelink is introduced besides an uplink and a downlink. The sidelink is a direct communication link between two terminals, and D2D communication is sidelink communication. The existing LTE V2X technology mainly uses the LTE D2D design as a reference, and also adopts a sidelink communication manner. FIG. 1 illustrates a schematic diagram of a deployment scenario of an existing V2V system.
There are usually three working scenarios for sidelink communication, i.e., In Coverage, Out of Coverage and Partial Coverage.
In the In Coverage scenario (i.e., a scenario with coverage of an LTE base station), the base station allocates a required sidelink resource to an OBU terminal at first, and then the terminal uses the resource allocated by the base station to transmit sidelink data and transmission parameters thereof.
In the Partial Coverage scenario (i.e., a scenario where the coverage of the LTE base station is unstable and signals are sporadic), the base station may not allocate the sidelink resource to the terminal dynamically and in real time, then the base station periodically broadcasts system information of a semi-static resource pool, and the OBU terminal may randomly select a sidelink resource from the resource pool to transmit the sidelink data and the transmission parameter thereof when getting out of the coverage as long as it receives information of the resource pool when being covered.
In the Out of Coverage scenario (i.e., a scenario completely without the coverage of the LTE base station), it is even impossible for the OBU terminal to occasionally receive the information of the resource pool in the system information of the base station. Under this condition, the sidelink data and the transmission parameter thereof may be transmitted only by randomly selecting a sidelink resource from a preconfigured resource pool statically stored in the terminal.
However, randomly selecting a sidelink resource from a resource pool to transmit sidelink data and transmission parameters thereof may inevitably bring resource conflict and interference between D2D/OBU terminals to cause reduction in the transmission success rate of the sidelink data. If the transmission success rate is increased by multiple retransmissions, the transmission delay may be increased. For achieving both of a high success rate and a low delay, the number of terminals transmitting sidelink signals at the same time within the same coverage is to be limited, which makes it difficult to implement high-capacity D2D communication and high-vehicle-flow V2V communication.
Therefore, for reducing interference between D2D/OBU terminals and improving sidelink communication efficiency, it is necessary to increase a proportion of an In Coverage scenario and reduce a proportion of an Out of Coverage scenario as much as possible. Coverage and capacity of a base station of a telecommunication operating company are planned according to a density distribution of terminals of a conventional type (for example, mobile phones), so that it is difficult to ensure that a D2D/OBU terminal is covered well. More seriously, if the telecommunication operating company is unwilling to perform base station upgrading and network optimization to support a D2D/V2V service in consideration of the cost, the D2D/OBU terminals may completely be in the Out of Coverage scenario, at this moment, LTE D2D and LTE V2V technologies may only adopt a resource pool random selection or LBT scheme, and their performance may also be unlikely to be higher than a pure Ad Hoc system such as IEEE 802.11p.